In general, this type of an image reading apparatus has been widely known as an apparatus in which a document image on a platen is irradiated with light, and its reflected light is read as an electric signal by a photoelectric conversion means. And each configuration of an apparatus for reading a document image arranged and set on a platen, and an apparatus for reading a document image moving on a platen at a predetermined speed has been known. As its reading optical system, a light path configuration with an optical system having the same magnification factor to guide a reflected light from the document image to a photoelectric conversion element, and a light path configuration with an optical system having a reduced magnification factor to guide it to a photoelectric conversion element have been known.
Conventionally, as such an apparatus, a monochrome image reading one or a color image reading one has been known. In case of the color, the photoelectric conversion element is configured by a color sensor, and in case of the monochrome, it is configured by a monochrome sensor. In either of these cases, when a gloss image is read, a problem arises in the accuracy of reading (contrast or the like) on a gloss region. That is, in case of a gloss image such as a photo image or a metallic print of gold or silver color print or the like, when a reading surface is irradiated with light from a conventional light source from an oblique direction, and then its diffuse reflection light is subjected to photoelectric conversion, then, the read data of an image of the gloss surface (region) is read as a dark data.
And so, for example, a patent document 1 (Japanese Laid-Open Patent Publication (Kokai) No. 2000-123152) has proposed a method in which a diffuse reflection light source for irradiating a document image with light from a direction declined by a predetermined angle with respect to the document image and a regular reflection light source for irradiating the document image with light from a vertical direction with respect to the document image are provided, and image data obtained by image reading using the light from the diffuse reflection light source and image data obtained by image reading using the light from the regular reflection light source are combined so as to obtain image data rich with reality such as texture, tone, or the like.
Also, a patent document 2 (Japanese Laid-Open Patent Publication No. 2006-126632) has proposed an apparatus in which a document image is irradiated with light from a declined direction and from a vertical direction with respect to the document image, and diffuse reflection light and regular reflected light are selectively guided to a photoelectric conversion means by switching between imaging paths for guiding the reflected light from the document image to the photoelectric conversion means.
And so, when one image data is to be obtained by photoelectric conversion data of each of the diffusion reflection light and the regular reflection light, conventionally, such as in the above-mentioned patent documents 1 and 2, a combining method is employed in which converted data from the diffuse reflection light and converted data from the regular reflection light are compared, and an output value (for example, data having a larger brightness) is determined to be the pixel data.
On the other hand, in such a type of an image reading apparatus, image data is obtained by correcting photoelectrically converted output value such as by shading correction, γ correction or the like for correcting distortion of image data due to time-dependent deterioration of a light source, deterioration of a photoelectric conversion element, or distortion of an imaging light path. In order to perform this shading correction, it has been known that a white reference plate is provided on a reading platen and a read-out output value (output value of a photoelectric conversion element) of a document image is corrected by its reference read-out value.